+ * d_ancestor - search for an ancestor
+ * @p1: ancestor dentry
+ * @p2: child dentry
+ *
+ * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
+ * an ancestor of p2, else NULL.
+ */
+struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
+{
+ struct dentry *p;
+
+ for (p = p2; !IS_ROOT(p); p = p->d_parent) {
+ if (p->d_parent == p1)
+ return p;
+ }
+ return NULL;
+}
+
+/*
+ * This helper attempts to cope with remotely renamed directories
+ *
+ * It assumes that the caller is already holding
+ * dentry->d_parent->d_inode->i_mutex and the dcache_lock
+ *
+ * Note: If ever the locking in lock_rename() changes, then please
+ * remember to update this too...
+ */
+static struct dentry *__d_unalias(struct dentry *dentry, struct dentry *alias)
+ __releases(dcache_lock)
+{
+ struct mutex *m1 = NULL, *m2 = NULL;
+ struct dentry *ret;
+
+ /* If alias and dentry share a parent, then no extra locks required */
+ if (alias->d_parent == dentry->d_parent)
+ goto out_unalias;
+
+ /* Check for loops */
+ ret = ERR_PTR(-ELOOP);
+ if (d_ancestor(alias, dentry))
+ goto out_err;
+
+ /* See lock_rename() */
+ ret = ERR_PTR(-EBUSY);
+ if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
+ goto out_err;
+ m1 = &dentry->d_sb->s_vfs_rename_mutex;
+ if (!mutex_trylock(&alias->d_parent->d_inode->i_mutex))
+ goto out_err;
+ m2 = &alias->d_parent->d_inode->i_mutex;
+out_unalias:
+ d_move_locked(alias, dentry);
+ ret = alias;
+out_err:
+ spin_unlock(&dcache_lock);
+ if (m2)
+ mutex_unlock(m2);
+ if (m1)
+ mutex_unlock(m1);
+ return ret;
+}
+
+/*
+ * Prepare an anonymous dentry for life in the superblock's dentry tree as a
+ * named dentry in place of the dentry to be replaced.
+ */
+static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
+{
+ struct dentry *dparent, *aparent;
+
+ switch_names(dentry, anon);
+ swap(dentry->d_name.hash, anon->d_name.hash);
+
+ dparent = dentry->d_parent;
+ aparent = anon->d_parent;
+
+ dentry->d_parent = (aparent == anon) ? dentry : aparent;
+ list_del(&dentry->d_u.d_child);
+ if (!IS_ROOT(dentry))
+ list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
+ else
+ INIT_LIST_HEAD(&dentry->d_u.d_child);
+
+ anon->d_parent = (dparent == dentry) ? anon : dparent;
+ list_del(&anon->d_u.d_child);
+ if (!IS_ROOT(anon))
+ list_add(&anon->d_u.d_child, &anon->d_parent->d_subdirs);
+ else
+ INIT_LIST_HEAD(&anon->d_u.d_child);
+
+ anon->d_flags &= ~DCACHE_DISCONNECTED;
+}
+
+/**
+ * d_materialise_unique - introduce an inode into the tree
+ * @dentry: candidate dentry
+ * @inode: inode to bind to the dentry, to which aliases may be attached
+ *
+ * Introduces an dentry into the tree, substituting an extant disconnected
+ * root directory alias in its place if there is one
+ */
+struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
+{
+ struct dentry *actual;
+
+ BUG_ON(!d_unhashed(dentry));
+
+ spin_lock(&dcache_lock);
+
+ if (!inode) {
+ actual = dentry;
+ __d_instantiate(dentry, NULL);
+ goto found_lock;
+ }
+
+ if (S_ISDIR(inode->i_mode)) {
+ struct dentry *alias;
+
+ /* Does an aliased dentry already exist? */
+ alias = __d_find_alias(inode, 0);
+ if (alias) {
+ actual = alias;
+ /* Is this an anonymous mountpoint that we could splice
+ * into our tree? */
+ if (IS_ROOT(alias)) {
+ spin_lock(&alias->d_lock);
+ __d_materialise_dentry(dentry, alias);
+ __d_drop(alias);
+ goto found;
+ }
+ /* Nope, but we must(!) avoid directory aliasing */
+ actual = __d_unalias(dentry, alias);
+ if (IS_ERR(actual))
+ dput(alias);
+ goto out_nolock;
+ }
+ }
+
+ /* Add a unique reference */
+ actual = __d_instantiate_unique(dentry, inode);
+ if (!actual)
+ actual = dentry;
+ else if (unlikely(!d_unhashed(actual)))
+ goto shouldnt_be_hashed;
+
+found_lock:
+ spin_lock(&actual->d_lock);
+found:
+ _d_rehash(actual);
+ spin_unlock(&actual->d_lock);
+ spin_unlock(&dcache_lock);
+out_nolock:
+ if (actual == dentry) {
+ security_d_instantiate(dentry, inode);
+ return NULL;
+ }
+
+ iput(inode);
+ return actual;
+
+shouldnt_be_hashed:
+ spin_unlock(&dcache_lock);
+ BUG();
+}
+EXPORT_SYMBOL_GPL(d_materialise_unique);
+
+static int prepend(char **buffer, int *buflen, const char *str, int namelen)
+{
+ *buflen -= namelen;
+ if (*buflen < 0)
+ return -ENAMETOOLONG;
+ *buffer -= namelen;
+ memcpy(*buffer, str, namelen);
+ return 0;
+}
+
+static int prepend_name(char **buffer, int *buflen, struct qstr *name)
+{
+ return prepend(buffer, buflen, name->name, name->len);
+}
+
+/**
+ * __d_path - return the path of a dentry
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry (may be modified by this function)